1. Field of the Invention
The present invention relates to an ink jet head, and, more particularly, to an ink jet head utilizing electrostatic force and a method of producing such an ink jet head.
2. Description of the Related Art
An ink jet head installed in an ink jet recording apparatus used as an image recording apparatus, such as a printer, facsimile machine, copying machine, or plotter, comprises nozzle holes to discharge ink droplets, discharging chambers (also referred to as pressurized chambers, pressurized liquid chambers, liquid chambers, or ink passages) communicating with the nozzle holes, and an energy generating unit for generating energy to pressure the ink in the discharging chambers. By driving the energy generating unit, the ink in the discharging chambers are pressurized, so that ink droplets are discharged through the nozzle holes. Normally, such an ink jet head is of an ink-on-demand type that discharges ink droplets only when ink is required for recording.
Japanese Laid-Open Patent Application No. 2-51734 discloses an ink jet head in which piezoelectric elements are employed as the energy generating unit for generating the energy to pressurize the ink in the discharging chambers. The diaphragms that forms the wall surfaces of the discharging chambers are deformed by the piezoelectric elements to change the content volume of the discharging chambers, thereby discharging ink droplets. Japanese Laid-Open Patent Application No. 61-59911 discloses an ink jet head in which a heat generating resistor is employed to heat the ink to form bubbles in the discharging chamber. The bubbles pressurize the ink so that ink droplets are discharged.
In the former ink jet head using the piezoelectric elements, however, the process of bonding piezoelectric chips to the diaphragms to give pressure to the discharging chambers is very complicated. Since an ink jet recording apparatus is required to perform a high-quality operation at high speed, it is necessary to employ a plurality of high-concentration nozzles in the ink jet head. However, the process of producing minute piezoelectric elements and the process of bonding a number of piezoelectric elements are very complicated and time-consuming. Furthermore, it is necessary to produce the piezoelectric elements in a thickness of approximately 30 to 150 xcexcm. However, with the conventional machine accuracy in size and shape, it is difficult to obtain uniform printing quality.
Also, in the latter ink jet head using the heat generating resistor, there is a problem that the heat generating resistor is damaged by the repetitive rapid heating and cooling, and by the shock at a time of bubble bursting. As a result, the life of the ink jet head becomes shortened.
To eliminate the above problems, Japanese Laid-Open Patent Application No. 6-71882 suggests an ink jet head in which the diaphragms that form the wall surfaces of the discharging chambers are deformed by electrostatic force so as to change the content volume of the discharging chambers, thereby discharging ink droplets. This ink jet head utilizing electrostatic force is advantageous in being small in size, having high density and high printing quality, and lasting for a long period of time.
In the ink jet head utilizing electrostatic force, it is necessary to apply an electric voltage from an external circuit to the diaphragms and the electrodes adjacent to the diaphragms so as to deform the diaphragms by electrostatic force.
Japanese Laid-Open Patent Application No. 9-307218 discloses an ink jet head in which a first substrate that forms diaphragms and liquid chambers and a second substrate that forms electrodes are bonded to each other. An external electrode for diaphragms (a diaphragm external electrode) is disposed on the upper surface of the first substrate, and external electrodes for electrodes (individual external electrodes) are formed in concave portions of the second substrate. Here, a vertical-direction distance between the diaphragm external electrode and the individual external electrodes are equivalent to the thickness of the first substrate. Therefore, a method in which a special-purpose FPC (Flexible Printed Circuit) cable having a top portion branched into two ends is used to have connection with an external circuit has been suggested.
However, having to connect the diaphragm external electrode to the individual external electrodes by the special-purpose FPC cable with the two branched top ends makes the connecting process troublesome and time-consuming. Also, the FPC cable is costly, and the production costs of the ink jet head are increased accordingly.
If the diaphragms and the electrodes are arranged at shorter intervals so as to obtain a high-density ink jet head, a yield decrease might be caused due to defective bonding or damage to the diaphragms when an electrode substrate is bonded to a silicon substrate as a diaphragm substrate having the diaphragms formed by performing anisotropic etching on the silicon substrate. Also, misalignment is often caused, and a number of bonding processes need to be performed. In view of this, this conventional ink jet head is not suitable for mass production.
On the other hand, if a silicon substrate is used as an electrode substrate while an n-type or p-type impurity layer is used as electrodes (as disclosed in Japanese Laid-Open Patent Application No. 6-71882), it is easier to form narrow gaps between the diaphragms and the electrodes than in the case where a metal film that might generate particles at the time of film formation is used. Also, a high-quality thermal oxide film can be formed as an electrode protection film on the electrodes. However, junction leak or punch-through between the electrodes is caused, resulting in poor reliability.
It is a general object of the present invention to provide ink jet heads and methods of producing the same, in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a high-density ink jet head having external electrodes that can be easily connected to an external circuit, and a method of producing this ink jet head without increasing the number of production steps.
The above objects of the present invention are achieved by an ink jet head having a diaphragm external electrode that located on the same plane as diaphragms. Accordingly, the ink jet head can be easily connected to an external circuit without using a special FPC.
The above ink jet head further includes individual external electrodes disposed within 2 xcexcm from the diaphragm external electrode, so that the ink jet head can be more easily connected to an external circuit.
In the above ink jet head, the individual external electrodes are aligned with the diaphragm external electrode, so that the ink jet head can be easily connected to an external circuit without using a special FPC.
In the above ink head, the diaphragms and the diaphragm external electrode are formed on a first substrate, the electrodes and the individual external electrodes are formed on a second substrate, and parts of the first substrate corresponding to the individual external electrodes on the second substrate are removed while the diaphragm external electrode is maintained. Accordingly, a decrease in yield due to defective bonding or damage to the diaphragms can be prevented. Furthermore, the formation of the diaphragm external electrode and the exposure of the individual external electrodes can be carried out at the same time.
In the above ink jet head, the diaphragms and the diaphragm external electrode are formed on a first substrate, and a metal layer is formed on the diaphragm external electrode. Thus, the corrosion resistance to etching of the ink jet head can be increased.
In the above ink jet head, the metal layer on the diaphragm external electrode has a multi-layered structure. Thus, the corrosion resistance can be increased, and the production costs can be reduced.
In the above ink jet head, a layer of the metal layer in contact with the first substrate is made of a metal that can be in ohmic contact with silicon. Thus, the contact resistance of the ink jet head can be reduced.
In the above ink jet head, the outermost layer of the metal layer is made of a metal that has resistance against an etching species based on halogen. Thus, the ohmic contact can be easily achieved while the corrosion resistance is maintained.
The objects of the present invention are also achieved by a method of producing an ink jet head, comprising the steps of:
bonding a first substrate having diaphragms and a diaphragm external electrode formed thereon to a second substrate having electrodes and individual external electrodes formed thereon, with a predetermined distance being left between each of the diaphragms and each corresponding one of the electrodes;
forming a contact portion having the same thickness as the diaphragms, the contact portion including at least a region on the first substrate corresponding to a region including the individual external electrodes on the second substrate and a part to become the diaphragm external electrode; and
removing the region of the contact portion except the part to become the diaphragm external electrode. In accordance with this method, an ink jet head having a diaphragm external electrode that can be easily connected to a connector such as an FPC can be obtained without increasing the number of production steps.
In the above method, the bonding step is an anodic bonding step that includes the steps of forming a SiO2-film gap spacer on the first substrate that is a monocrystal silicon substrate, or forming concave portions in the second substrate that is a glass substrate, so that the predetermined distance is maintained between each of the diaphragms and each corresponding one of the electrodes. Thus, an ink jet head having a diaphragm external electrode that can be easily connected to a connector such as an FPC can be obtained without increasing the number of production steps.
In the above method, the bonding step includes the steps of:
forming a SiO2-film gap spacer in the first substrate that is a monocrystal silicon substrate and/or in the second substrate that is also a monocrystal silicon substrate; and
bonding the first substrate and the second substrate directly to each other, so that the predetermined distance is maintained between each of the diaphragms and each corresponding one of the electrodes. Accordingly, an ink jet head having a diaphragm external electrode that can be easily connected to a connector such as an FPC can be obtained without increasing the number of production steps, and narrow gaps can be formed with great precision.
The above method may further comprise the step of forming a protection film having resistance to etching on the part to become the diaphragm external electrode, prior to the removing step. Accordingly, etching margins can be increased, and excellent ohmic contact can be achieved.
The above method may further comprise the step of forming a protection film having resistance to etching in the region other than the region to be removed from the first substrate by etching, prior to the removing step. Accordingly, etching can be performed without a mask. Thus the production costs and the number of production steps can be reduced. Also, a decrease in yield can be restricted. Furthermore, the bonding of liquid chambers formed on the diaphragm substrate becomes easier, and the wettability can be increased.
In the above method, the relationships
(a/x) greater than 1 and
(a/y) less than 1,
are satisfied, wherein: x represents a short side of an opening of each of the diaphragms; y represents a short side of the contact portion; and a represents a thickness of the first substrate. Accordingly, etching can be performed without a mask, and the production costs and the number of production steps can be reduced. Also, a decrease in yield can be restricted. Furthermore, side etching can be avoided, and contamination on the bonding surfaces of the liquid chambers formed on the diaphragm substrate can be prevented.
In the above method, when etching is performed on the first substrate, a part between the part to become the diaphragm external electrode and the adjacent individual external electrode is maintained. Accordingly, the size the diaphragm external electrode can be desirably controlled.
In the above method, the relationships,
(a/x) greater than 1,
(a/z) greater than 1, and
(a/y) less than 1,
are satisfied, wherein: x represents a short side of an opening of each of the diaphragms; y represents a short side of the contact portion; z represents a short side of the diaphragm external electrode; and a represents a thickness of the first substrate. Accordingly, etching can be performed without a mask, and the production costs and the number of production steps can be reduced. Also, a yield decrease can be restricted.
The above method may further comprise the steps of:
forming a p-type or n-type impurity layer on a part of each of the electrodes adjacent to each corresponding one of the diaphragms;
forming a heat-resistant film on the contact portion; and
forming a connecting hole between the impurity layer and the heat resistant film. Accordingly, the reliability of the electrode substrate can be increased.
The objects of the present invention are also achieved by a method of producing an ink jet head, comprising the steps of:
bonding a silicon wafer that is a first substrate having diaphragms and a diaphragm external electrode formed thereon to a second substrate having electrodes and individual electrodes formed thereon;
performing etching on the first substrate, leaving a contact portion including a region corresponding to the individual external electrodes on the second substrate and a part to become the diaphragm external electrode;
cutting the silicon wafer into head chips; and
removing the region corresponding to the individual external electrodes from the contact portion. Accordingly, an ink jet head having high reliability can be obtained at low production costs.
In the above method, when the diaphragm external electrode is formed, a metal layer having a low etching rate compared with silicon is formed on the part to become the diaphragm external electrode. Accordingly, the first substrate can be protected from corrosion when the diaphragm external electrode is formed on the first substrate.
In the above method, an etching mask made of a material that does not generate a product is used. Accordingly, the reliability in connection with a connector can be increased.
In the above method, the etching mask may be made of quartz. Accordingly, the reliability in connection with a connector can be further increased.
In the above method, the etching mask may be made of alumina. Accordingly, the reliability in connection with a connector can be further increased.
Other objects and further features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.